Geographic Range

Ochlerotatus dorsalis is a widespread species of mosquito that occurs in the northern hemisphere including Europe, Central Asia, China, Northern Russia and North America. Ochlerotatus dorsalis is most commonly found in North America and Europe from Scandinavia to Greece. (Becker, et al., 2003)

Habitat

Ochlerotatus dorsalis has a wide range of habitat all over the northern hemisphere. Along with many other Ochleratatus species, O. dorsalis lives primarily in salt marshes, littoral habitats and inland habitats. Larvae live in small bodies of water and swamps as well as temporary bodies of water formed by rainfall, melted snow and floods. Ochlerotatus dorsalis occurs near humans because they are the main source of bloodmeal for female mosquitoes. Ochlerotatus dorsalis lives in a variety of different habitats including grasslands, coastal areas, forests, tidal areas, and marshes. These habitats must have a standing water source of some kind in order for pale marsh mosquitoes to reproduce. (Becker, et al., 2003; Milankov, et al., 2009)

Physical Description

Ochlerotatus dorsalis is recognizable by its scutal markings and coloration that forms a dark brown median stripe that extends to the prescuttal stripes, which are lighter in color. The female has a proboscis which is covered in dark scales and the wing veins are predominately covered in light scales. The abdominal terga, tergites or sections of the abdomen, of the female have a white stripe running longitudinally and may not be present on all segments. Males are similarly colored but have smaller proboscis with larger setae surrounding it. Setae are bristly, hair-like structures that are used for protection in mosquitoes. Adults usually reach a length of around 16 mm and can weigh as much as 2.0 mg. This species displays sexual dimorphism in that females are typically larger than males.

Larva are distinguished by short antennae, a siphon with 4 to 5 branches and a rounded anal papillae. The siphon is used for breathing air while the larvae are underwater. (Becker, et al., 2003)

Development

The eggs of Ochlerotatus dorsalis are laid in any small open body of water or swamp. The females lay their eggs individually in the mud of these habitats before the winter. Females may oviposit in saline or fresh water bodies but salt water is preferred. The aquatic eggs overwinter and hatch into larvae at the first signs of warm weather. The larvae remain underwater to grow and develop. Larvae feed on suspended particles in the water by filter feeding at the top or bottom of the water column. The larvae then molt into pupae where they do not eat and stay inactive until completely molted into the adult form. After the transformation is complete, the adult splits the pupa shell and emerges. Total development time takes 7 to 10 days under optimal conditions. ("Mosquito Notes: A Pale Marsh Mosquito", 2008; Becker, et al., 2003)

Reproduction

In spring or early summer, males gather to form large swarms which attract females. It is not known how the males know to swarm or why the females are attracted to them, but swarming does seem to be the most common mating style exhibited by all Culicidae. All species of Ocherlotatus are known to swarm while mating. Ochlerotatus dorsalis females will most likely mate more than one time, but will only do so after all of her eggs are laid. (Purdue University Medical Entomology, 2010; Takken, et al., 2006)

Mosquitoes in general, as well as Ochlerotatus dorsalis, mate seasonally. In the spring or early summer, O. dorsalis males will form large swarms to attract females. Within a swarm, males can sense females by wing beat frequencies and species specific chemicals. Ochlerotatus dorsalis females require only one mating to fertilize her lifetime store of eggs. Fertilization takes place internally and females can hold the sperm until they are ready to lay their eggs. Ochlerotatus dorsalis is capable of long flight paths and can lay its eggs 5 to 15 miles away from breeding or feeding areas. Females must take a blood meal in order for the eggs to develop.

Ochlerotatus dorsalis breed during spring and summer, which varies geographically.

Range age at sexual or reproductive maturity (female)

7 to 10 days

Range age at sexual or reproductive maturity (male)

8 to 12 days

Parental involvement is nonexistent in Ochlerotatus dorsalis. Females lay their eggs singularly in the ground along the sides of standing water sites. The females leave after ovipositing and the eggs hatch into larvae which make their way to the water to complete development. (Becker, et al., 2003)

Parental Investment

no parental involvement

Lifespan/Longevity

Ochlerotatus dorsalis have delayed-hatching eggs which do not hatch until the soil conditions have reached a certain temperature and moisture content. The eggs of O. dorsalis have an overwintering period where they stay dormant in the soil until spring arrives. Larva and pupa stages last 7 to 10 days under optimal conditions. It can take up to two days to complete the pupal stage. Ochlerotatus dorsalis has a typical lifespan of two months in the summer, although some can hibernate and live up to six months. ("Mosquito Notes: A Pale Marsh Mosquito", 2008; Becker, et al., 2003; Purdue University Medical Entomology, 2010)

Range lifespanStatus: wild

2 to 6 months

Behavior

Ochlerotatus dorsalis has characteristic habitats of open fields, forests and coastal areas. Here female pale marsh mosquitoes search for warm-blooded hosts when the temperature is in the range of 9 to 32 degrees Celsius. Peak biting frequency usually occurs in the late afternoon and early evening, but O. dorsalis can be active into the night also. They are most active on calm or cloudy days. Searching for bloodmeal during the day may also occur in open fields. Females are primarily exophagic (feed outside), but will enter tents and houses to feed.

Female Ochlerotatus dorsalis are vicious biters that leave painful bites on the skin of their hosts. The females feed mostly on mammals including humans, squirrels, chipmunks, deer and livestock, but will also feed on birds. Males are not parasitic and feed mostly on nectar, pollen or fruit for nutrition. They have no need for a blood meal because they are not incubating eggs. Males may follow the females post-mating up to 20 miles away. Larvae live in stagnant ponds or other small bodies of water. They do not breathe oxygen from the water, but instead use a siphon to breathe air from above the surface. They will float just under the surface of the water and filter feed. There are 4 larval stages that are dependent on the amount of food, crowding and water temperature. Pupae will also stay in the water and breathe air by coming to the surface. ("Mosquito Notes: A Pale Marsh Mosquito", 2008; Becker, et al., 2003; Purdue University Medical Entomology, 2010)

Home Range

Ochlerotatus dorsalis is a very strong flier which allows it to have a very large home range. Females can fly up to 20 miles to disperse their eggs. Males will sometimes accompany them on these flights. Pale marsh mosquitoes usually breed in marshy areas that have been recently flooded. ("Mosquito Notes: A Pale Marsh Mosquito", 2008; Carpenter and LaCasse, 1955)

Food Habits

The adult female Ochlerotatus dorsalis is a parasitic sanguivore, meaning it drinks blood as its main food source. Males are nectarivores that drink nectar from plants, plant sap and honeydew produced by aphids. The males do not drink blood at all. Some females may be nectarivorious if there is not a blood meal present. These females can still produce eggs, but the development of the egg will depend on energy stores of the mother. Females who do feed on blood will do so on mammals, including humans, chipmunks, squirrels and livestock, and some will obtain their blood meal from birds.

Larvae feed by filter feeding in the water by using specialized "gills" to trap food particles. The Ochlerotatus dorsalis larvae stay on the surface of the water and breathe oxygen using a siphon, and filter out the food particles by sending them past the mouthparts where they are eaten. The food usually consists of algae, small living organisms, and parts of plant or animal material. Larval development is dependent on the amount of food it consumes. ("Mosquitoes of Public Health Importance and their Control", 1993; Purdue University Medical Entomology, 2010)

Predation

General predators of mosquitoes include bats, birds, dragonflies and fish. Fish that live in the water where O. dorsalis larvae are present may feed on them. Mosquitofish are common predators of pale marsh mosquitoes due to their ability to withstand various water conditions.

Ecosystem Roles

Ochlerotatus dorsalis females are parasitic insects that use many mammals including humans as hosts. Birds may also be parasitized, though not as frequently. Female pale marsh mosquitoes may cause certain habitats to become uninhabitable if the swarms become too great. Host species cannot live in these areas due to the painful bites inflicted by the mosquitoes. Ochlerotatus dorsalis males do not take blood meals, but instead feed on plant sap and nectar. Pollination may occur from feeding on the nectar of flowers, but they are not main pollinators. (Becker, et al., 2003; Purdue University Medical Entomology, 2010)

Economic Importance for Humans: Positive

Economic Importance for Humans: Negative

Ochlerotatus dorsalis has many negative effects on humans. The largest being painful bites inflicted when females feed on hosts' blood. These bites are common on other mammals and birds. Due to their vicious biting, areas where pale marsh mosquitoes are present can be rendered uninhabitable for humans and other animals. This species can be very detrimental to livestock, leading to reduced feeding and dangerous behavior from attempting to escape the attacks. In addition to its extremely painful bites, Ochlerotatus dorsalis is a vector of many diseases. These diseases include West Nile virus, Western equine encephalitis virus, St. Louis encephalitis virus, and California encephalitis virus. The Japanese encephalitis virus and the bacteria Francisella tularensis (causing tuleremia) are also carried by O. dorsalis. Some of these diseases affect humans and animals while some only affect animals. The Western equine encephalitis virus is a disease of livestock that can cause significant destruction. ("Mosquito Notes: A Pale Marsh Mosquito", 2008; Becker, et al., 2003; Purdue University Medical Entomology, 2010)

Contributors

Eric Dryer (author), University of Michigan-Ann Arbor, Heidi Liere (editor), University of Michigan-Ann Arbor, John Marino (editor), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor, Rachelle Sterling (editor), Special Projects.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

acoustic

uses sound to communicate

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

crepuscular

active at dawn and dusk

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

filter-feeding

a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

freshwater

mainly lives in water that is not salty.

herbivore

An animal that eats mainly plants or parts of plants.

internal fertilization

fertilization takes place within the female's body

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.

marsh

marshes are wetland areas often dominated by grasses and reeds.

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nectarivore

an animal that mainly eats nectar from flowers

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

seasonal breeding

breeding is confined to a particular season

semelparous

offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

suburban

living in residential areas on the outskirts of large cities or towns.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention. Mosquitoes of Public Health Importance and their Control. Atlanta, Georgia: Public Health Practice Program Office. 1993.

Disclaimer:
The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.